DC (Direct Current)-DC converters may be found in many electronic devices. For example, DC-DC converters are often found in PDAs (Personal Digital Assistant), cellular phones and laptop computers. These electronic devices often contain several sub-circuits with different voltage level requirements from that supplied by a battery or an external supply. A DC-DC converter converts a source of direct current from one voltage level to another voltage level in order to meet the voltage levels required by sub-circuits.
One method of providing DC-DC conversion is through the use of a linear regulator. However, a linear regulator may dissipate too much heat for devices such as laptop computers and cellular phones.
DC-DC switching converters convert one DC voltage level to another by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors) or a combination of both. These conversion methods are more power efficient (often 75% to 98%) than a linear regulator for example. This efficiency is beneficial to increasing the running time of battery operated devices.
A DC-DC step-down converter converts a higher voltage to a lower voltage. For example, on an IC (integrated circuit) a 3.6 volt power supply and a 1.8 volt power supply may be needed to provide power to circuits on the IC. In this example, a DC-DC step-down switching converter may be used to convert the 3.6 voltage reference to a 1.8 voltage reference.
When a DC-DC step-down switching converter is initiated, the voltage on the output of the DC-DC step-down switching converter may not be zero. Rather, the output of the DC-DC step-down switching converter may be pre-biased to voltage greater than zero. The output of the DC-DC step-down switching converter may have been pre-biased to a voltage greater than zero by another circuit. When a DC-DC step-down switching converter starts with a pre-bias voltage on its output, the voltage on the output may temporarily drop causing problems for the circuits connected to the output.